Field of the Invention
The present invention relates to an imaging device.
Description of the Related Art
There is known a device which measures the oxygen saturation of blood, that is, the ratio of concentration of oxygenated hemoglobin to the sum of oxygenated hemoglobin and reduced hemoglobin by using a plurality of near-infrared light beams. A pulse oximeter and light topography are representative medical devices which use the oxygen saturation of blood.
Japanese Patent Laid-Open No. 2005-95606 discloses a pulse oximeter which obtains the oxygen saturation of arterial blood at high accuracy by removing the influence of body motion artifacts. This pulse oximeter receives five light beams of different wavelengths, and removes the influence of a variation in arterial blood and a variation in tissue based on a change amount of reflected light or transmitted light of each wavelength output from a light receiving unit.
Japanese Patent Laid-Open No. 11-297973 describes an infrared imaging device including a first light receiving unit for receiving mid-infrared light and a second light receiving unit for receiving far-infrared light.
The device described in Japanese Patent Laid-Open No. 2005-95606 cannot specify the positions of the first and second portions having different wavelength characteristics in an object including the first and second portions. In the device described in Japanese Patent Laid-Open No. 11-297973, the first and second light receiving units are stacked. Therefore, the wavelengths of light beams respectively received by the first and second light receiving units are required to be apart from each other like mid-infrared light and far-infrared light. It is thus difficult for the device described in Japanese Patent Laid-Open No. 11-297973 to accurately separate and detect the first and second portions each having a local maximum value of the absorbance in the near-infrared wavelength band.